Question

Could you separate a colloid by filtering? Explain

Answer 1

Not easily but it depends on the type of colloid.

Explanation:

If you have a solid in liquid colloid, then it is not possible to separate it by filtration using conventional filter papers as even using the smallest pore size paper you are only just about reaching the maximum particle size of a colloid. Colloids have particle sizes between 1 and 1000 nm (0.001 - 1.0 `mu`m) and the finest grade filter paper has mean particle size 2 `mu`m.

It may be possible to do it with ultra-filtration, whereby the pore size of filter paper is reduced by soaking the paper in a solution of something such as collodion or gelatine, and then hardening them by soaking in formaldehyde. If you use a series of graded ultra filter paper, it is possible to separate colloidal particles of different sizes.

If, however, you have a liquid/liquid colloid (like an emulsion) then filtering won't work as the "particles" are not actually solid.